US2667534A - Electrical system - Google Patents

Description

Jan. 26, 1954 E. M.' cREAMER, JR., ETAL ELECTRICAL SYSTEM 5 Sheet's-Sheei 1 Filed Aug. 4, 1951 Jan. 26, 1954 E. M. CRE-AMER, JR., ETAL 2,667,534

ELECTRICAL SYSTEM 3 Sheets-Sheet 2 Filed Aug. 4, 1951 ELECTRICAL SYSTEM 3 Sheets-Sheet 3 Filed Aug. 4, 1951 ATT Patented Jan. 26, 41954 UNITED STATES PATENT OFFIQ Philadelphia, Pa., assignors to Philco Corporation, Philadelphia, Pa., a corporation of Penn- Sylvania Application August 4, 1951, Serial No. 240,324

18 Claims.

The present invention relates to cathode ray tube systems and more particularly to cathode ray tube systems in which the position of the electron beam relative to a beam interceptive structure of the tube is indicated by an indexing member so arranged in cooperative relationship with the beam interceptive structure as to pro- -duce a signal Whose time of occurrence is indicative of the time at which the cathode ray beam attains a predetermined position.

There are a variety of circumstances in which it is desirable to produce and to utilize signals Whose times of occurrence are indicative of those times at which a cathode ray beam attains predetermined positions. For example, in the copending application of David E. Sunstein, Serial No. 185,106, iiled September 15, 1950, and assigned to the assignee of the present invention, there is described a color television image presentation system utilizing a single cathode ray tube having a screen member comprising vertical stripes of luminescent materials which respond to electron impingement to produce light of three different primary colors. These stripes are preferably arranged in laterally displaced color triplets, each triplet comprising three vertical phosphor stripes producing light of different primary colors. The order of arrangement of the stripes may be such that the normally horizontally scanning cathode ray beam produces red, blue and green light successively upon impingement of successive stripes. Such a cathode ray tube may be incorporated in a color television receiver which produces three separate video signals, each indicative of a different primary color component of a televised scene, which signals are sampled sequentially and utilized to control the intensity of the cathode ray beam. For proper color rendition, it is then required that, as phosphor stripes producing each of the primary colors of light are impinged by the cathode ray beam, the intensity of the beam be simultaneously controlled in response to the contemporaneous value of the video signal representing the corresponding color component of the televised scene. However, since the rate at which the beam scans across the phosphor stripes of the screen may vary due, for example, to nonlinearity of the beam deflecting signal, the times at which the samples of the several video color signals should be taken will generally not occur exactly periodically. To effect proper timing of the sampling operations, it is therefore desirable to derive signals indicative of the instantaneous position of the cathode ray beam upon the image forming screen and to utilize these so-called indexing signals to control the times at which the samplings of the several color signals are eiected. Although certain of the systems embodying the invention which are described hereinafter are of the type that utilize the signals indicative of the beam position for purposes of timing the sampling of color signals in a color television receiver, it Ywill be obvious from the following that the invention is in no way dependent upon such use, and that the signals produced by the arrangement of the invention may be utilized for other purposes as well. For example, use may be made of the invention in controlling the times and rate of occurrence of intervals at which a signal is representative of color information in the case Where the signal has been previously sampled at an independently determined rate so as to be initially representative of color information at independently determined intervals. Again, use may be made of the invention in effecting linearization of the deiection of a cathode ray beam, in a system according to the disclosure of copending U. S. application of Wilson P. Boothroyd, Serial No. 219,093, led April 3, 1951, and assigned to the assignee of the present invention.

In the copending application of Carlo V. Bocciarelli, Serial No. 198,709, led December 1, 1950, and assigned to the assignee of the present invention, there is described and claimed a cathode ray tube system in Which the indexing signal hereinbefore mentioned is derived from a plurality of stripe members arranged on the beam intercepting screen structure, which members comprise a material having secondary emission properties which differ from the secondary emission properties of the remaining portions of the beam intercepting structure. The indexing stripe members are arranged each over a corresponding phosphor stripe serving to generate one of the primary colors, so that, when the beam impinges upon the phosphor stripe, the indexing member is simultaneously excited and the resultant secondary emission produces a pulse in a suitable output circuit.

In the case of a cathode ray tube system for color television, the indexing member may consist of a material of high atomic number, such as gold, platinum or tungsten, or it may consist of certain mixtures including magnesium or magnesium oxide, and the remainder of the beam intercepting structure may be provided with a coating of a material having a detectably different secondary emission ratio, such as aluminum, which coating also serves as a light reecting mirror for the phosphor stripes in accordance With well known practice.

Because of the high accelerating voltages of the order of 10 to 20 kilovolts normally used in the systems under consideration, the difference in secondary emission between the indexing stripes and the aluminum coating is relatively small, and in many instances there exists the danger that the normally detectable difference in voltage appearing at the collector electrode system may be masked or at least contaminated by spurious voltages. example, from the video signal itself which appears in the collector electrode system because of the fact that the collector electrode signal voltage is a function of the intensity of the cathode ray beam and in the normal course of events the cathode ray beam is intensity modulated by the video signal at the time that the beam impinges on the indexing stripe member.

It is, accordingly, a principal object of the invention to provide a cathode ray tube system of the type in which the position of the electron beam relative to a beam intercepting member is indicated by an indexing member and in which a clearly defined indexing signal voltage is generated. I

A further object of the invention is the provision of a cathode ray tube system in which the indexing signal voltage generated is substantially free of spurious signal voltages.

A further object of the invention is the proe vision of a cathode ray tube system which permits simple and inexpensive separation of the video and indexing signals, whereby an index signal Voltage substantially free of video components, or

indeed of any other extraneous components, is obtained.

To achieve the foregoing objects as well as others which will appear, systems constructed in accordance with our invention employ a cathode ray tube having disposed therein a beam interceptive structure comprising beam position indicating or indexing elements arranged in predetermined geometric relation to other portions of the beam interceptive structure. These beam position indicating elements are characterized by having values of secondary emission ratio which differ from those characterizing other regions of the beam interceptive structure, when electrons of the cathode ray beam impinge thereon. By

reason of these characteristics, as the beam is swept across the screen structure so as to traverse the boundaries between regions of different secondary emission ratio, a signal voltage is generated in the output collector electrode having variations corresponding to the differences between the secondary emission ratios. However, since the voltage at the collector electrode-is also a function of the intensity of the beam, and also because of random noise voltages generated by the beam, the signal voltage produced contains spurious signal components constituted by video and by noise modulation of the beam intensity. Attempts at separating, from the several voltage components appearing in the collector electrode circuit, those components which are due only to variations in secondary emission ratio have been complicated by the fact that components produced by such variations in secondary emission ratio lie in substantially the same frequency range as do components produced by video or noise modulation of the beam. Instead of attempting such separation, a system embodying our invention incorporates a source of periodic carrier signal voltage of a frequency substantially different vfromany frequency which the Video 75 Such spurious voltages may derive, for 1 beam modulating signal may assume. This signal voltage is applied to the beam intensity control grid of the cathode ray tube together with the video signal, care being taken to keep the amplitude of this carrier signal voltage suiciently small so that its fluctuations will produceno substantial departures in the light emitted by the tube screen structure from that due to Video modulation of the beam in the absence of carrier. As a result of the application to the beam intensity control grid of this additional signal Voltage, there appear, in the collector electrode circuit, signal voltage components which vary in proportion to the beam intensity variations produced by this additional signal voltage. Furthermore, the amplitude of these latter variations are caused to change in proportion to variations in secondary emission of the screen structure as the electron beam is sweptacross regions of different secondary emission ratios. t is apparent that the signal components produced in the collector electrode circuit by this additional carrier signal voltage, and which are. amplitude modulated in accordance with the rate of traversal of indexing elements in the screen structure, are readily separable from similarly modulated. video and noise components simply by virtue of the fact that these are in a substantially different frequency range as a result of the selection of the frequency of this additional signal voltage in the manner hereinbefore mentioned. The only additional step required to produce an indexing signal, uncontaminated by the aforesaid video or noise components, is the detection of this index modulated carrier signal voltage so as to reproduce a signal voltage which varies only in proportion to variations in emission as the electron beam sweeps across regions of different secondary electron emission ratio. The particular manner of the operation and construction of various systems embodying our invention is set forth at length in the following description of certain representative embodiments which will be readily understood by reference to the accompanying figures wherein:

Figure 1 illustrates a fundamental form which systems embodying our Vinvention may take;

Figure 2 is a greatly enlarged, fragmentary View of the screen structure of the cathode ray tube incorporated in the system of Figure 1;

Figure 3 illustrates a preferred embodiment of the invention wherein the aforementioned source of carrier signal voltage is utilized to overcome certain deficiencies arising from otherwise unavoidable time lags associated with index controlledV color systems in addition to performing its essential role in the purification of these index signals; and

Figure 4 illustrates the embodiment of our in-I vention in another type of color televisionreceiver possessing certain advantages. v

Referring now to Figure l, the embodiment of the invention shown therein comprises a cathode ray tube I0 which is equipped with a AconventionalV cathode i l, beam intensity control grid l2, focus coil i3, horizontal and vertical deflection coils i4 and an accelerating anode i5 which consists of ai. conductive coating on the inner wall of the envelope and which terminates at a point spaced from the Vface plate i t of the tube in conformance with well established practice. First anode i3 is connected to Ia suitable source of focusing curf rent i3d, while accelerating anode i5 is suppliedv from a suitable source of positive potential A++.l

Deflection coils ld are supplied with conventional horizontal and vertical deflection signals, respecfm tively, from horizontal and vertical deflection cir-l cuits I'I. The elements of tube I0 hereinbefore listed are all entirely conventional, as are the power supply and deflection circuits connected therewith, so that no further discussion thereof is required.

The face plate I5 of the tube is .provided witha beam intercepting structure I 8 shown in detail in Figure 2. In the arrangement shown in Figure 2, the structure I8 is formed directly on the face plate I6. However, it should be well understood that the structure I3 may be formed on a suitable light transparent base which is independent of the face plate I6 and may be spaced therefrom. In the arrangement illustrated, the face plate I6, which in practice consists of glass having preferably substantially uniform transmission characteristics for the various colors in the visible spectrum, is provided with a plurality of elongated parallelly arranged groups of stripes I9, 2B and 2l of phosphor material which, upon impingement by the cathode ray beam, iluoresce to produce light of three different primary colors. For example, the stripes I9 may consist of a phosphor which, upon excitation, produces red light, the stripes 26 may consist of a phosphor which produces green light and the stripes 2l may consist of a phosphor which produces blue light. Each of the groups of stripes may be termed a color triplet and, as will be noted, the sequence of the stripes isrepeated in consecutive order over the area of the structure I8. Suitable materials constituting the phosphor stripes IS, 2!) and 2l are well known to those skilled in the art, as well as the method of applying the same to the face plate I6 and further details concerning the same are believed to be unnecessary.

The beam intercepting structure I8 further comprises a thin, electron permeable conducting layer 22 which is arranged on the phosphor stripes I9, 20 and 2| and which preferably further constitutes a mirror for reflecting light generated at the phosphor stripes toward face plate I6. In practice the layer 22 is a light reflecting aluminum coating which is formed in a well known manner. It should be well understood, however. that other metals having similar characteristic properties may also be used. Such other metals are, rfor example, magnesium or beryllium.V f

Arranged over one of the phosphor stripes ofV each of the color triplets (for exampleV over each of the green phosphor stripes 2G) is an' indexing stripe 23 consisting of a material having a secondary emission ratio detectably. different from that of the material of coating 22. Each stripe 23 may consist of a metal of high atomic number, such as gold, or of a mixture containing mag nesium oxide as previously pointed out.

It should be kept in mind that the screen structure of Figure 2 is shown as it would appear viewed from the interior of the cathode ray tube. When so viewed, the electron beam of the tube will ordinarily scan thescreen from right to left,`

stripes in the 6.. details of construction of this screen 'structure' I8, reference will, thereforabe had to Figure 2.

The accelerating anode I5, in addition to performing the usual electron beam accelerating function, also functions to collect secondary electrons emitted by screen structure I8 in response to impingement by the electron beam. The secondary electron emission circuit associated with the screen structure is closed by output resistor 34 which interconnects anode I5 and screen structure I8. 1

By way of this secondary electron emission circuit, there are derived, from thescreen structure, signals indicative of beam impingement upon indexing stripes 23. The manner of derivationof these signals is novel and is therefore fully set forth hereinafter. The manner of utilization of these signals, on the other hand, is conventional and will therefore bebriefly reviewed so asto complete the groundwork on which to base a complete understanding of our inventive concept.

As is frequently the case in color television receiver systems, the system illustrated in Figure lV is supplied with three separate received signals, respectively indicative of the red, green and blue components of the televised scene, which signals preferably have had their D.C. components restored and are of such polarity that the more positive portions thereof correspond to darker re'-v gions of the television image. These different signals are next recurrently sampled, in a predetermined order, so as to form a single signal, Whose amplitude is, at time-spaced intervals, representative of intelligence respecting different ones of the three primary color vcomponents of the televised scene. This single signal is then applied to cathode ray tube grid I2 where it controls the beam intensity. It is desired to have the sampling operation occur at such intervals that the resultant single signal will be representative of intelligence respecting a particular color at the exact time when the electron beam is impingent upon a stripe emissive of light of that same color. To achieve this result, it has been proposed to control the sampling operation by means of the signals derived from the indexing stripes, for these signals are indicative of the actual time of such impingement. A

In the embodiment selected for illustration in Figure 1, the sampling operation is carried out by three sampling circuits, 25, 25 and 2'! to which the three received color signals are respectively supplied. Sampling circuits of the type here contemplated are well known in the art and each one may, for example, consist of a conventional pentode vacuum tube, to one of whose control grid electrodes the received video signal is continuously applied, while its other control grid electrode is normally biased so far negatively as to prevent space current from reaching the anode. These other electrodes of the pentode sampling tubes are now supplied, in the proper sequence, with positive gating signals of sufficient magnitude to overcome their negative bias and to permit conduction of the tubes. In the present arrangement, these gating signals are derived from a three phase generator 28, having three output terminals 29, 3Q and 3l at which gating signals differing mutually in phase by appear respectively. The nominal frequency at which the sampling operation is carried out is preferably coordinated with the rate of beam sweep traversal across color stripes of the cathode ray tube screen structure. A typical nominal value of sampling frequency is 7 megacycles for asomar.

each. color. signal; The instantaneous. sampling frequency will; of course, be directly controlledI by:Vv the' `signalsI which are derived: from. theY indexing stripes; of' the tube: screen. for` this very purpose.

It; has been foundi advantageous to. deal with theY sampled color'signals ati the lowest. possible frequency. For this. reason, the output signals of the red; green and blue samplersarenot. ap-Y pliedY directly tothe control. grid. electrode l2.v of. the cathode ray tube but are instead passed:

through. a. conmionl 10W-pass` filter 32 whose frequency response'is such; that it will transmit. only signals: the; U'to 7 megacycle frequency range;

Thus,. instead of a series-of discontinuousfsignals; therewill be supplied, to control grid electrode. i2; a smoothly Varying 7 megacyclesignal Whose' amplitude. is the` same as the amplitudes of' the individual sampled signals .would have been at their sampling intervals. beam intensity will be controlled smoothly and continuously, and yet accurately in accordance With color information; instead of beingA subject to the undesired transient effects of discontinu.- ous modulation.

Assuming that the component color input sig.- nals suppliedV to the samplers 25, 26 andk 2! were produced. by a predetermined systematic scan'- ning; operation,v so that at successive instants their values are representative of ther colors of different elements'of a televised image, and that the-horizontal andv vertical deflection circuits il are designed and controlled so as to reproduce that scanning; process,- then a. corresponding color. image'will be reproduced on` the beam intercepting structure I8 of tube I0.

It Will be understood that, instead of sampling each received signal with" pulse-like signals occurring at the proper times,` it is' possible to pro duce a single signal of the desired time-sequential form by forming three sinusoidal signals, as by genera-tor 28; havingythe same mutual phase relationships as the different samplingv signals hereinbefore described, and then modulating the signal. in each color channel with the appropriately phased oneof these sinusoidal signals.

For the purpose of producing the aforementioned indexing signals, the system of Figure 1.

is, according to the invention, further provided with a carrier Wave generator 33, a secondary t electron emission output circuit which includes the cathodeiray screen structure, its accelerating anodel and output resistor 34, a filter 35 and a detector 313.

In: the operation ofv the cathode ray tubel systemv thus far described, the cathode ray beam,`

inits vertical and horizontal travel across the beam intercepting structure i8 (see Figure 2), impinges successively'on the coating 2v2 and the indexingv stripes 23, causing a secondary emission current to flow throughy output resistor 3d.

This currentis relatively small when the beam is impingent upon the coating 22 but increases substantially whenv the beam impingesupon an indexing stripe 23. Thus, the current. flowing through output resistor 34 Will iiuctuate, during scanning of the screen structure by theelectron beam, in proportion to variations in secondary electron emission therefrom as the beam traverses alternateregions of low and high secondary electron emissivity.

As the beam thus scans across the screen struc'- ture;.its'intensity is modulated in accordance'with color information by the. color signalv applied to Consequently, theV S' pla-ined;v This variation ofi beam'. intensity.' will', of' course, also produce variations inV secondaryI emission from. the'. screenv structure. As; aresult, the Variationsv in currentl iiovving: throughv4 output. resistor 3d'. Will also-bely proportional to the=.varia.= tions in this signal voltage. It is in this manner. that the indexing signal produced inoutpu-tiresistor 3d by the passage ofthe beamacross suoi cessive indexing stripes. and intervening regions of loW secondary electroni emissivity.' ist'. coni:-I taminatedY with video signal-1 variations, asfhere inbefore indicated..

Inr accordance with the invention;` there is supe plied to the controligridelectrode l2'of cathode'l ray tube IB, in addition to any video or noise" voltagesV which may appear.' thereon, an. independently generated. carrier wave voltage pro.` duced by generator 33; This generator may; take` anyA conventional form provided'on'ly that it be.

. proportioned so as tooperate stably ata substan tially constant frequency. An electron-coupled"v Hartleyv oscillator has been successfully used in. actual embodiments. rIhis generator is` so, Y` con.- structed asA to producea carrier WavevoltageLhave .z ing a frequency substantially outside. the range` of frequencies occupied by the Video signal. In the present illustrative case, thisvideosignal hasy been assumed to occupy a frequency range: of from Oto-7 megacycles. In that event, the car;-v rier Wave frequency may be chosen to be 3.825 megacycles, it being understood` that this..A is: a. figure selected from considerations of practical convenience. Any other frequency' substantiallyhigher than the highest video'frequencyrv will?. be

appropriate i" or the same purpose.

It will noW be apparent that this carrier Wave"r Voltage Will also produce corresponding variations. in the emission of secondary electrons from screen structure I8 and, since this carrier Wave'voltage. is applied continuously to the control. grid elec-- trode, these variations will also be subject to the superimposed variations due to, changes in the secondary electron emission from the screen structure as the electron beam passes across al'- ternate regions of low and high emissivity. ThusE there Will appear across output resistor 34. avoitage component which is proportional'not only to.v

thecarrierwavevoltage but also-to variationsin.

secondary emission. from the screen structure l producedby electron beam scanning thereof. In

other Words, there Will appear across output: re.- sistor 34, a voltage component of carrier wave freiquency, which is amplitude modulated. at theratev at which the electron beamI sweeps across indexing elements ofthe screen structure.

As was explained.' in the courseA of the: del scription ofl Figure 2, the indexing stripesy 23 are preferably disposed at every thirdicolor stripe, or in thev present case, at every successiveV stripe emissive of green light. By virtue of the particular rate at which the sampling of the received'- color signals is carried out, informationrespecting the green color signal will be recurrent in thel video signal applied' to beam intensity controlV grid I 2 at a 7 megacycle rate. Thereforethe fiori-- zontal and vertical' deflection circuits will be so preadjusted as to produce beam deflection acrosssuccessive green light emissive color stripes at a nominal rate of 7megacyc1es. As a result, thel rate of vbeam traversal of indexing stripes super:- imposed on these green color stripes will al'sobe 7- megacycles, on the average and thisiwill', furthermore, be the nominal frequency of the signalpro-v duced in output resistor 34 byksuch indexing stripe control. grid r2` inthe manner hereinbefore ex- 715': traversal. This 7"megacycleindexing-signal will however vary in instantaneous frequency because of non-linearities in the deflection circuits which cause the rate of beam traversal across consecutive indexing stripes to depart from the desired 7 megacycle rate in an unpredictable manner and also because of virtually unavoidable inequalites in indexing element spacing which occur when working with the close tolerances required inthe construction of the screen structure I8. It has been found practical, however, to limit departures from the nominal 7 megacycle frequency of the indexing signal variations to a range of not more than 10% on either side of this nominal rate. Thus the rate of variation of the output signal across output resistor 34 due to scanning of the beam across indexing elements can reliably be expected to be somewhere in the frequency range of 6.3 megacycles to 7.7 megacycles. As a result, there will be a component of output voltage, produced by interaction between Variations proportional Vto carrier wave voltage variations .and variations proportional to index signalvariations, which will occupy a frequency range centered about the difference between 38.5 megacycles and '7 megacycles, or 31.5 megacycles, and extending 0.7 megacycle on either side of this center value. Furthermore, if the electron gun characteristic is linear, there will be in this frequency range no component of output voltage due to video signal variations.

.Filter 35, of any conventional design suitable for the purpose, is connected to output resistor 34, this lterbeing so proportioned as to transmit only signal components in the aforesaid frequency range of 31.5 megacycles plus or minus 0.7 megacycle to the substantial exclusion of all other signal components. There then appears, at the output of filter 35, a single modulation component produced only by interaction between the 38.5

megacycle carrier wave voltage and the voltage variations due to scanning of the beam across indexing stripes of the screen structure. This output is then supplied to detector 3S which is operative to select from this modulated signal, only the low frequency modulation envelope which, as

has been seen, corresponds to the signal variations produced by changes in secondary emission from the screen structure I3 as the electron beam traverses consecutive indexing stripes 23. One convenient way in which this may be accomplished is by supplying to detector 36, not only the modulation component transmitted by filter 35, but also the signal produced by carrier wave generator 33, and arranging detector 35 to heterodyne these two supplied signals and to select, for further transmission to its output circuit, the low frequency heterodyne component corresponding to the aforedescribed signal variations produced by the indexingV stripes. By virtue of its time and rate of occurrence, this signal thus provides an indication of the time and rate at which the electron beam of the cathode ray tube is impingent uponv an indexing element 23 of the screen structure. Similarly it provides an indication of the time when the electron beam is impingent upon the green light emissive phosphor stripe which lies directly beneath each indexing stripe. Furthermore, assuming reasonably accurate maintenance of spacing between colored light emissive phosphor stripes in each triplet, the occurrence of the indexing signal may also be taken as an indication of the time of beam impingement upon the following two phosphor stripes of the triplet, inasmuch as such impingementlwill take place at l0 flxedly time-spaced intervals from the occurrence of the indexing signal.

Before proceeding, it may be pointed. out that the aforedescribed heterodyne process is not the only one by which the pure indexing signal may be derived from the screen structure of the tube. Alternatively, filter 35 may be modified so as to transmit not only the single 31.5 mc. difference frequency component produced by interaction between carrier wave signal and Variations due to the screen structure, but also the sum frequency component at 45.5 megacycles and the carrier wave component at 38.5 megacycles. In that event, heterodyne detection of the indexing signal is not required. Instead, detector 36 may simply be a conventional amplitude-modulation detector of any well known type arranged so as to detect the relatively low frequency '7 megacycle modulation component due to the indexing elements of the screen structure.

In any event, it is the output of this detector which is applied to three phase generator 28 to control the rate of gating signal production of the latter. In the .present arrangement, the three phase generator 28 may be so arranged that a gating signal which is in phase with the indexing signal supplied to the generator will appear at output terminal 30 and will therefore be supplied to green sampler 23 so that a signal indicative of green video information will be applied to the beam intensity control grid electrode I2 of cathode ray tube i0 at the time when the cathode ray beam is impingent on a green light emissive phosphor stripe of the screen structure I8.

A variety of arrangements are known which will serve in the capacity of three phase generator 28. One such may comprise an automatically variable delay line with three output taps so spaced that signals applied to its input appear at the different taps in the aforementioned 0, 120'? and 240 phase relation irrespective of the frequency of the input signals. As indicated in the discussion of Figure 2, the beam, in its traversal of the screen structure, will next impinge upon a red light emissive color stripe. Furthermore, since the phosphor stripes are approximately equally spaced, this impingement will occur approximately one third of the way through the interval between consecutive indexing signals. Accordingly, three phase generator 28 is constructed so as to produce an output signal at terminal 3i at a time which is later than that at which it produces asignal at terminal 30 by one-third the interval between successive index-y ing pulses. In other words, the output signal at terminal 3l will lag by 120 degrees the output signal at terminal 30. This signal is then applied to red sampler 25 where it serves to gate on the sampling tube, thereby permitting a signal in#- dicative of red color information to appear at the grid i2 at the time when the cathode ray beam is impingent upon a red phosphor stripe of the screen structure. Continuing its progress across the screen structure, the electron beam will next impinge upon a blue light emissive phosphor stripe and this will occur two-thirds of the way through the interval between two consecutive indexing signals. lTherefore blue sampler 21 must be actuated at that particular time and for this reason three phase generator 28 is adapted to produce an output signal at terminal 23 which is delayed by 240 degrees in phase with respect to the output signal at terminal 30, which latter, in turn, is in phase with the indexing signal.

acentos 11 finus, it is seen that each indexing signal initiates the production by three phase generator 2.8Y of threev consecutive output signals occurring. in order at terminals 3o, 3l and 2.9 and differing mutually in phase by 120 degrees. Any change in either the spacing of the phosphor stripes across the screen structure or in thelinearity oi `beam deflection will then be accompaniedby a change in the time and rate of occurrence of the indexing signals and this will in turnproduce an appropriate change in the output of three phase generator 253v which will insure that the sampling circuits areractivated atv the proper times so that a signal representative of a desired color Will appear at the beamI intensity control grid` electrode l2 at the time when the cathode ray beam is impingent upon a phosphor stripe emissve of that color.

Although in the embodiment of Figure l,Y aswell as in those to follow, the indexing signal is derived, from the screen structure by relyingv on differences in secondary emissivity between different portions of the screem it will be understood that this is by no means the only way of deriving such indexing signals. A Well known alternative, for example, resides in disposing a photoelectric cell in screen confronting relationship and equipping the, same with a filter transmissive of light from only one type of color stripe. Such a` system is subject to all the aforementioned shortcomings or the secondary emission system and its indexing signal is susceptible to the same remedial measures.,

Observe now that, in thel arrangement of Figure l, the indexing signal derived from screen structure E8 passes, in succession,y through index output resistor 34, filter 35 and detector ed, after which it is utilized to trigger three phase generator 2B Whose output signals, in turn,- sample the red, green and blue signal information so, as to produce a single signal which is, at recurrent time intervals, representative of intelligence respecting the three diierent primary colors. As has been pointed out hereinbefore, the entire purpose of this` system is to insure that the intervals at which this signal isl representative of such color intelligence will occur exactly when the beam is impingent upon corresponding colored light emissiye phosphor stripes. It is apparent that, the greater the number of components through which theA indexing signal must pass and the greater the number of operations performed thereupon or which are dependent thereon for their initiation, the less likely7 it will be that this coincidence willv actually bemaintained. For, while, it is ordinarily assumed that the passage of a signal through various circuit components is substantially instantaneous, nevertheless it is recognized that under conditions where extreme accuracy must be maintained. the. transient or response time of such components` may assume disturbing proportions. In the case under consideration,l for example, the. response. of the three phase generator .'23 to an, applied indexing signal may not be as rapid as desired, with the result that the sampling of the color input signals` may occur a trifle later than the times indicated by the occurrence of the indexing signal. Cbviously, the result of thiswould be that the beam intensity would not correspond exactly to color information at the time when the beam is impingent upon colored light eniissive phosphor stripes so. that color distortion of thel image formedon the: screen structure will result. .It is therefore` desirable, to haveY the indexing.y signal and all signals, derived therefrom. or initiated cuit components prior to its actual control, of the. rate of occurrence. of intelligence representative intervals inv the. video signal as nnally applied to the beamV intensity control grid electrode of thecathode ray tube.

A` system embodying our invention and which is considerably superior to4 that of Figure l in this respectI is. illustrated in Figure 3,y to 'which more detailed reference may now be.. had. Note, first of all, that important portions of the. system of Figure 3 are identical with, certain portions of that of Figure '1, Similar elements of the two systems have,I therefore, been designatedV by similar reference numerals. ThusY the system of Figure 2, like that of Figure. lis, provided with a cathode. ray. tube l0. having cathode Il, beam intensity control grid l2., focus coil i3, deflection circuits 14 accelerating anode i5,A face plate 6', and. a screenl structure L8 which may be identicah in every respect.. with that, of Figure 2, so that no'detailed` description of this screen, structure, is required.. Conventional powery supply and deflection circuitsY are again pro,.- vided for cathode, ray tube 19 these including horizontal' and vertical deiiection circuits l'l and sources of focus current and accelerating4 anode potential. The secondary emission circuit, of the screen structure is again, as in Figure l,- closed by an output resistor 34 connectedl between; the screen structure i8 and'y the accelerating anode l5. The beam intensity control grid', Ilz is sup.- plied with video signals., derivedina manner hereinafter explained' in detail andA is also supplied with a carrier wave signal voltage produced by carrier wayeoscillator 33'Which iss'imilar to the similarly numbered oscillator off Figure l. As was the case in Figure 1 these simultaneously applied video signals and carrier wave signals interact with variations. in secondary emission produced'l by sweepingY of' the beam across alternate regions of highv and low secondary emission ratio to produce signal voltage components across index output resistor 34' which are the result of modulation of' the video signal by. variations in secondary emission due to the. indexing structure, as Well asother signal components which, are the result of modulation ofY the carrier'wave in accordancewith, secondary emission variations produced` by the` indexing struc-- ture. Assuming again as was the case in the system or'V Figure 1', a maximum video, modulation frequency of '7 megacyclesl and an indexing, structure so proportioned as to producea 'I'megacycle modulation, due to. beam traversal oil' the indexing structure alone, .the modulation com-- ponents produced,V by. index modulation ot thev carrier wave voltage will. again be at. a4 Substantially different4 frequency from those produced by indexing signal modulation of the video sig.- nais.

Just as was done, in the system of Figure 1, these amplitudeA modulated carrier wave com.-

, ponents, or better yety a single heterodyne coma signal deriyedv directly from; canfiei' waveos:v cillator; 33v4 would. now: be; supplied; to the SGQndiinput circuit of mixer 31 for heterodyning with the indexing signal component selected by filter 35 to produce a signal representative of indexing information alone, in this arrangement the signal to be applied to the second input circuit of mixer 31 is derived in a different manner. Specifically, the carrier wave oscillator output signal is supplied, simultaneously with its application to beam intensity control grid I2, to a three phase signal generator 33 which is similar to three phase generator 28 of Figure 1 except that it is constructed so as to produce gating .signals at each of its output terminals 39, 40 and 4I at a rate determined by the frequency of the carrier wave oscillator signal voltage. Note that it is now possible to use a simple constant delay device as the three phase generator since the input signals supplied thereto are always of the same frequency. Assuming the same values as in the example of Figure l, where the carrier wave oscillator operated at a frequency of 38.5 megacycles, signals mutually diifering in phase and each recurrent at a 38.5 megacycle rate will then appear at three phase generator terminals 39, 40 and 4|. These signals are now used to activate, respectively, the red, green and blue signal sampler 25, 2B and 21 which may be substantially similar in construction to the similarly numbered samplers of Figure 1. The output signals of the three samplers are then additively combined and supplied to a filter 42 which is arranged to transmit a band of frequencies whose Width is equal to the maximum range of any one of the individual color input signals prior to sampling and which is centered about 38.5 megacycles. Thus there will appear, at the output of filter 42, a 38.5 megacycle carrier signal modulated in amplitude and phase in accordance with the time-multiplexed red, green and blue color signals.

It is this signal, transmitted by lter 42, which is supplied to the second input circuit of a conventional mixer 31 where it is heterodyned with the output signal of filter 21. Since this latter is at a nominal frequency of 31.5 megacycles, as

has been indicated, the resultant output of mixer 31 will be a '1 megacycle signal modulated in accordance with the variations due to the timemultiplexed red, green and blue signals. A filter 43 may be provided to select the low frequency sidebands of the output of mixer 31, and the output of this lter is then suitable for application to the beam intensity control grid l2 of cathode ray tube l0, being representative of color information at three properly time-spaced intervals during each cycle of the 7 megacycle indexing signal, as required for faithful color reproduction.

It has been found that while, in systems such as those shown in both Figures '1 and 3, indexing impurities due to video modulation at the screen structure are substantially eliminated, nevertheless some contamination of the indexing signal may be produced by interaction between the video signal voltage and the carrier wave signal voltage at the cathode and control grid electrode of the cathode ray tube unless certain precautions are taken. Such interaction is due to non-linearity in the grid control circuit and will produce spurious signal components at the difference frequency between the two applied signals. These, in turn, will be reproduced in the index signal output circuit. Since these spurious components are thenat the same frequency-as the components which it is desired to derive from this same indexing output circuit, they will not be rejected by subsequent frequency selective networks like filter 35 and may therefore succeed in contaminating the final indexing signal.

To overcome this difficulty, there is inserted `in the cathode circuit of the cathode ray tube a resistor 44, across which portions of the aforedescribed spurious components will be developed. The voltages so produced across resistor 44 are then amplified in cancellation amplifier 45 which is a conventional vacuum tube amplifier arranged to transmit only the aforesaid spurious components with such gain that subsequent application thereof with appropriate phase to resistor 46, located in the index signal output circuit, will just cancel those spurious components which appear in this index output circuit as a result of the aforedescribed phenomenon.

For further details of the treatment of this phenomenon by means of signal cancellation, reference may be had to the copending U. S. patent application of William E. Bradley, Serial Number 203,175, filed December 28, 1950, and assigned to the assignee of the present invention. Alternatively, two separate cathode ray guns may be employed within the same cathode ray tube envelope, one of them producing a beam which is modulated in intensity by the carrier wave signal voltage exclusively, while the other one is modulated only by the video signal. In that event, of course, there will be no interaction between the two signals at the electron gun and the aforedescribed cancellation circuit will not be Y required. This expedient constitutes a separate invention which is fully described and claimed in copending application Serial No. 242,264, led August 17, 1951, of Melvin E. Partin which is likewise assigned to the assignee of the present invention.

Note, further, that non-linearities in the cathode ray tube gun structure may produce beam intensity modulation at harmonies of the video signal applied to the control grid. The carrier wave frequency is therefore preferably chosen so that neither it, nor the frequencies of signals resulting from index modulation thereof are at harmonics of the video signal. This is the principal consideration which prompted the particular choice of carrier wave frequency in the present case, as 38.5 megacycles is midway between two harmonic frequencies of the '7 meg-acycle video signal and so are its index modulated sidebands at 31.5 and 45.5 megacycles.

In the systems illustrated in both Figures l and 3, the red, green and blue color signals initially applied to the systems have been assumed to be cf the form of signals produced, for example, by three simultaneously scanning television cameras, equipped with red, green and blue light transmissive lters, respectively, and'all viewing the same scene. Signals of this type are,-of course, directly available in laboratory equipment and may also be readily provided in closed circuit commercial equipment. When, however, the originally produced camera signals are to be transmitted tc distant receivers by means of broadcasting facilities, there is ordinarily not sufficient spectrum bandwidth available to be able to transmit these three signals simultaneously in their original form. Consequently, expedients have been devised for modifying these signals at the transmitter so as to conserve bandwidth while retaining all useful intelligence content. While it is, of `course, always possible to reconstituteired,

greengand ibiuefsig-nals-.zat :the receiver l.which are of :the same :form aswthose produced lby theeameraafthereby v:providing:color :input .signals of the type :required .for appiicationxto the .system `of either Figures 1 or 3, it Willzordi-nani'lylbe advantageous, 'from-:the point of viea1 of equipment economy, .to ntiliaezthereeeived signals as nearly as feasible .their :actual received form. It behooves, therefore, to examine the applicability of :our inventive concept .to presently proposed systems .forthe receptioneand .utilization of color telerision :signals to rwhich [certain bandwidth economyrtechniques Vhave .been applied.

l.The .technique ,for effecting such bandwidth economy VWhich has-received .the most favorable notice :uprto the present time is :one in which the aforesaid .three .separately 'produced color signals are sampled at 'the :transmitter at Asome lrapid rate, such as, forexample,f3.5 megacycles. By then .gadditiyely combining 'the sampled signals andpassing fthein'through a low pass filter adapted to transmit, forrexample signal components inthe range'from Oto 4 megacycles, there is produced,;at the output of the filter, a composite signal having a'slowly 4varying component which corresponds tothe averagebrightness'of the televised scene and which .occupies the to 3 megacycle frequency range, .upon which there is sup-erimposed 'a :high :frequency .color component of 3L5 :megacycle Anominal frequency. This color component is :phaser-and amplitude modulated in accordance with .color .information so that its sideba-nds `occupy .the '3 Ato 4 megacycle range. het itzbeunderstood, in this connection, that the particularmethod'hy Wh-i'ch'a signal of the general Ytype hereinbefore set forth is `produced at the .transmitter.isimmateriaL our only concern being with the form vof vthese signals as they appearzatthe receiver.

In the copending U. S. application of Robert C. Moore, :Serial No. 214,995, i'lled March 10, '1951, and assignedto the assignee of thepresent invention, there isaset vforth in detail va'television receiver vsystem adapted .to be .supplied With video signals having the general'forrn hereinbeforeoutlined. Thisnsystern utilizes indexing signals derived from the screen structure of the receiver cathode ray tube for the purpose of modifying the :rate ofoccurrence of intervals during which therreceived'signal-is representative of Ydifferent .l

component color information, so that these intervals are .caused to coincide Withintervals during Which'the vcathode ray :beam isimpingent upon screen elements emissive of .light of the proper color. vThe:manner in which .our inventive concept inay .be directly applied, with highly benecial effects, toa system ,of the type disclosed in the last-.named copending application Will .now bedescribed withparticular'reference to Figure 4 of -the drawings. There is shown, in Figure 4, a cathode ray tube i8 identical with the similarly designated cathode ray'tube of Figures 1 and 3, in that it too commises a cathode H, control grid electrode i2, fofcuscoil I3, horizontal and vertical deiiection circuits M, laccelerating anode I5, face plate l `andscreen structure I8. Like the cathode ray tubes of.Figures land 3, it is also connected vto suitable sources yof focus current |I andfac'celerating anode potential A++, as Well as to 'conventional horizontal and vertical deiiectionfcircuits i?. rihe secondary emission circuit of Yscreen structure .I8 is again vclosed by a resisterV 3s `internonnecting the accelerating anode andthe.screenfstructure ,.A'lter 35, substantialiy :identical ywith vthose similarly kdesignated 36 filters Figures Til :andi 3 isizconnected .receive the `signal devteloped aacross output resistor est. A2335 megacycle carrier Wavetsignal .is produced carrier wave oscillator:33Y and .is'appliedwto control grid. electrode t2 of cathode .ray tube -lll by'ivayiofansa'dding circuitf'i .in which it isadditively-.,cornbined .withfother :signal components Ito be described in '-nioreadetail hereinafter. :Assin eac-h .of the vpreviously .described embodiments, this Ycarrier WaveI :signalliproduces:corresponding variations in the potential :acrossoutput-resistor '34, :these variations .libeing modulated ati the 'rate of traversal .of Vindexingstripes in the fscreen structure .it by the Yelectron bearnzas the atter is .deflected .across fthe .screen structure. *'.Thus there Willa-gain appear heterodyne components produced fby this :modulation across output iresistor 3Q, filter i235 zabeing, .asiusual, arranged to derive therefrom .the diff erence frequency heterodyne component. Assuming ragain :that the iindexing stripes Yof 'the screen structure :are :so spacedin relai-,ion tothe. speed. yrif-beam traversal due to vdeflection thereof acrossithe-screenstructure .Las .to .produce a'modulation :of .the lcarrier Wave at they rate of L'Imegacycles, Athen this difference 'frequency componentfselected lby filter :35 will again 'be Eat .a nominal 31:5 megacycle frequency. 'Beforeeonsidering thetpathV followed 'by this modulation eomponent through .the freinainl der of the systemyit wiil'be necessary to consider the composition treatment of the video signal in more. detail. The entire "receivedsyideo signal will appear at the output cfa vdeosignal source i8 Wherethere Wilfl bezavailable-theOto-F3 magacyeleferightness signal,the to lin'i'egacyclecolor signal, `as Well as conventional 7-blanking and: syn-Y chronizing signals 'interspersedtherewith in the usual manner. lNote, in-'tli'is-connectiomthatthe colorsignal'a-lone :provides no indication ofthe actual times of occurrence of .the :intervals during eachlcycle of thisco'lor signal at'vvhich its amplitude is actually Irepresentative Aof color information. Consequently, vit' is common `practice to provide intermittently recurrent oscillatory signal bursts `of short duration having the same nominal frequency as'that of color signal and having 'a phase, with `reference `to thep'hase of the color signal, which is'indicative of theactual times of occurrence of colorrepresentative intervals inthe latter. "In orderto make these oseil latory `signal bursts, which are called color-synchronizing bursts, greedily' distinguishable 'from' the actual color signal, they are 'frequently superimposed Aon 'the trailing portion'of the horizontal blanking pulses, Whose 'leading portion is, of course, occupied by the `conventional line syn#v chronizing pulse. As in 'the system .disclosedin Figure l of the aforementioned copending :application of Robert C. Moore, the yvideo signals appearing-.at the output ofvi'deo signal source-48, and hai/ving the aforedescribed charaster-isties, are 'divided' among three Aseparate signal channels in the following manner. vThe low frequency or brightness components Vof 'the composite signal are separated from'the'remainder of the signal by -a low pass filter Ei9 vvWhich transmissive Yof signal components in the 0to3 'megacycle range to the substantial exclusion'of s'igna'lso'f all other frequencies. "The high "frequency color compo` nent ofthe composite's'ignal 'isseparatedfrom all other components by means of ahigh pass filter 5t arranged to transmit only signals above three megaeycles in frequency. "Finallygthe color-syn-fl chronizing, burstsare-separatedffrom the remaim der -of the composite -signalby flrst=appl3,fing 'this composite signal to a blanking pulse gating circuit I which is amplitude discriminatory to transmit only signals superimposed on the blanking pulse. rI'hus this gating circuit will transmit only the horizontal synchronizing pulses and the color synchronizing bursts, these being the only signals whose amplitude level exceeds that of the blanking pulses. The output of this blanking pulse gating circuit is then supplied to a color burst separator 52 which may simply consist of a lter adapted to pass signals of megacycle frequency to the substantial exclusion of all others, thereby rejecting the horizontal synchronizing pulses which occur at a much lower rate, namely 15.75 kilocycles according to present-day television standards. The color synchronizing bursts, Which will now appear at intervals of one horizontal scanning line in the output of color burst separator 52,-are next utilized to operate a cohered oscillator 53 which produces a continuous signal, also of 3.5 megacycle frequency and having the same phase characteristics as the color synchronizing bursts.

There are thus available, in three separate channels, the separated low frequency brightness component, the high frequency color component, and a continuous signal having the phase characteristics of the color synchronizing bursts. Reference to the above-mentioned copending application of Robert C. Moore will show that the treatment of the video signals has, up to this point, been exactly the same in the present arrangement as in that of Figure 1 of the above-mentioned copending application. In the latter arrangement, the continuous signal produced by the counterpart of cohered oscillator 53 was heterodyned With an indexing signal derived from the tube screen structure, after which one of the heterodyne components produced was heterodyned with the high frequency color component to produce a nnal output signal of index frequency which had all the phase and amplitude information of the original color signal in the form of corresponding phase and amplitude modulation. The iinal output signal thus produced was then representative of color information at discrete intervals which, however, recurred not at the rate determined by the received signal but instead at the rate and at times determined by the indexing signal. In the present arrangement the signal appearing at the output of lter 35, unlike that produced in the Moore embodiment, is not of a frequency determined solely by the physical arrangement of the indexing stripes in the cathode ray tube and the rate at which the electron beam traverses them, but is further dependent 'oni the frequency of the carrier wave from oscillator 33 which is supplied to the grid of the cathode ray tube l0 together with the video signal. However, this signal contains indexing information in the form of a heterodyne between a signal representative of such information and the aforementioned carriervvave signal and it may therefore be supplied to mixer 54 along with the output from cohered oscillator 53 in a manner and for a purpose similar to that of Moore. There is then selected, from the output of mixer 54, one heterodyne component produced in response to the aforesaid input signals. Preferably, this Will be the sum frequency component or, under the present illustrative conditions, the 35 megacycle component. This frequency selection will ordinarily take place in the conventional tuned output circuit of the mixer 54. However if this circuit proves not to be sufficiently sharply frequency discriminatory. additional filters may be provided as required. This 35 megacycle heterodyne output component kof mixer 54 is next supplied to another mixer 55. This latter is preferably of the balanced type characterized in that only heterodyne components produced by the mixer appear in its output circuits while components of the input signal frequency proper are suppressed. Balanced mixer 55 is simultaneously supplied with the high frequency color signal derived from high pass filter 55. These two input signals are heterodyned by the mixer and from its output there is selected the difference frequency heterodyne component or, in other Words, a signal of 31.5 megacycle nominal frequency which is now phase and amplitude modulated in proportion to the phase and amplitude modulation of the high frequency color signal so as to produce modulation sidebands extending over a 0.5 megacycle range on either side of the aforesaid nominal frequency. This output signal of balanced mixer 55 is next supplied to still another mixer 56 where it is heterodyned with a signal derived directly from carrier Wave oscillator 33, there being provided, in the output circuit of mixer 56, a band-pass lter 51 which is arranged to select, from among the output components of mixer 55, the difference frequency component which lies in the '7 plus or minus 0.5 megacycle frequency range.

Thus, there appears at the output of bandpass filter 51 a signal of the nominal frequency of the signal produced by the indexing stripes of the screen structure of the cathode ray tube lil but bearing the same phase and amplitude information as the received high frequency color signal. Consequently, there will be three intervals during each cycle of this 7 megacycle signal at which the signal will be representative of color information. Thus, Whereas the received color signal Was representative of color information three times during each 3.5 megacycle signal cycle, the modified color signal will be representative of color information 3 times during each 7 megacycle signal cycle. Variations in this nominal 7 megacycle rate will occur because of departures in the indexing signal from its ideal 7 megacycle rate brought about by non-linearity of the sweep trace or inequality of color stripe spacing. In spite of such variations, the color signal produced by bandpass filter 51 Will be precisely right for application to control grid electrode I2 Where it will serve to produce a beam intensity corresponding to the proper color information at the very interval when the beam is impingent upon a phosphor stripe emissive of that particular color. This particular topic is treated at length in the aforementioned copending application of Robert C. Moore Where a substantially identical modified high frequency color signal is finally produced. Again, as in the aforementioned copending application, this color signal is now additively combined with the low frequency brightness signal derived from low pass filter 49, this being accomplished in adding circuit 41 Where, as previously indicated, there is also added the carrier Wave signal Voltage produced by oscillator 33. The recombined low frequency, high frequency color and carrier Wave signals are then utilized to control the beam intensity by means of control grid I2. v

Thus it is seen that our inventive concept is readily applicable tosystems in Which the applied signal is exactly of the form in which it may normally be expected to arrive from a broadcasting station. Naturally, numerous modificationsof the systems hereinbefore illustrated Will occur vto those skilled in the art Without departing from the scope of our inventive concept. Therefore, We desire the latter to be limited only bythe appended claims.

We claim:

l. In a cathode ray tube system: a cathode ray tube comprising a source oi an electron beam and a beam interceptive structure including a fluorescent screen structure and also having nrst and second portions, said portions being responsive to beam impingement to produce outputs which vary in response to variations in beam intensity, the relationship between said outputs `and the intensity of said beam being different for said first and second portions; meansl for deecting said beam to impinge said beam successively upon said rst and second portions of said beam interceptive structure; a source of an image signal comprising' components within a predetermined frequency range; means responsive to said image signal to modulate the intensity of said beam to control the light emission from said fluorescent screen structure, modulation also producing variationsv in the outputs of said portions comprising frequency components Within said range; means for modulating the intensity of said beam at a frequency external to said range, said last-named modulation and the successive impi'ngements of said beam upon said first and second portions cooperating to produce variations in said outputs comprising frequency components external to said range; and means for deriving from said outputs a signal representative solely of variations in said outputs comprising frequency components external to said range.

2. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptiv'e structure having first and second portions, said portions being responsive to beam impingement to produce outputs which vary in response to' variations in beam intensity, the relationship between said outputs and the intensity of said beam being different for said rst and' second portions; means for def-looting said beam to impinge saidbeam su"- cessively upon said nrst and second portions of said beam interceptive structure; a source of an image signal comprising components within a predetermined frequency range; means responsive to said image signal to modulate the intensity of said beam, said modulation producing variations in the outputs of said portions comprising frequency components Within said range; means for modulating the intensity of said beam at a frequency external to said range, said last-named modulation and the successive impingements of said beam upon said first and second portions cooperating to produce variations in said outputs comprising frequency components external to said range; and means for deriving from said outputs a signal representative solely of variations in said outputs comprisingA frequency components external to said range.

3. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptive structure including a iiuorescent screen structure and also having rst and second portions, said portions being responsive toY beam impingement to produce outputs which vary in response to variations in beam intensity, thel relationship between said outputs and the intensity of said beam being different for said nrst and second portions; means for deflecting said beam to impinge said beam successively upon said iirst and second portions of said beam interceptive structure; a source of an image signal comprising components Within a predetermined rst frequency' range; means responsive to said image signal to modulate the intensity of said beam to control the light emission from said fluorescent screen structure, said modulation and the successive impingement of said beam upon said first and second portions also producing variationsl in the outputs of said portions comprising frequency components Within a predetermined second range; means for modulating the intensity of said beam at such frequency that said last-named modulation and the successive iinping'ernents of said beam upon said rst and second portions cooperatively produce variations in said outputs comprising' a frequency component' external to both said predetermined ranges; and means for deriving from said outputs a signal representative solely of variations in said outputs comprising frequency components external to both said ranges.

4. In a cathode ray tubeE system: a cathode ray tube comprising an electron interceptive structure, means for projecting electrons towards said structureI means for controlling the' path follovvedv by said projected electrons so as to impinge said electrons upon a small region of said structure, said structure including a fluo'- rescent screen structure'- and also' having first and second portions, said portions' being responsive to electron impingement to produce outputs which vary response tof variationsin the number of electrons" impingent thereon, the relationship between said outputs and the said nurnber of impingent electrons' being differentv for saidrfirst and second' portions; means for de'- fle'cting said electrons to impi ge said electrons successively upon'- Said iirst sind' Second portions of said' electron intercptive structure; a source ofV an image signal comprising components vvithin a predetermined frequency range; means responsive to said iinag'e signal to modulate the number of electrons impingen't upon said structure to control the light emission from said fluorescent, screen structure, said modulation also producing' variations in the outputs of said portions comprising frequency components within said range; means for" modulating the said number of impingent electrons at a frequency external to said range, said'last-named modulation and the successive impingements of said electrons upon said first and second portions cooperating' to produce variations in said outputs comprising frequencyqcomponents external to' said range; and meansl for deriving from said outputs a signal representative solely of variations in said output comprising frequency components externall` to said range.

5`. In a cathode ray-r tube system: a cathode ray tube comprising'a source of an electron beam and a beam' interceptive structure including a fluorescent screenstructure and also having first and second portions, said portions being responsive to beam impingement to produce outputs which vary in responseto variations in beam in'- tensity, the relationship between said outputs and' the' int'ei'sity of: saidV beam being different for said first and second'portions; means for deflecting said beam to inipnge saidl beam successively upon said nrst and second portions of said beam interceptive structure; a source of an image signal comprising components Within a predetermined frequency range; means responsive to said image signal to modulate the intensity of said beam to control the light emission from said iiuorescent screen structure; means for modulating the intensity of said beam at such a frequency that said last-named modulation and the successive impingements of said beam upon said first and second portions cooperatively produce variations in said outputs comprising a component at a frequency external to said predetermined range and different from harmonic frequencies of said image signal components; and means for deriving from said outputs a signal representative solely of variations in said outputs comprising frequency components external to said range.

6. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptive structure including a iiuorescent screen structure and also having first and second portions, said yportions being responsive to beam impingement to produce outputs which vary in response to variations in beam intensity, the relationship between said outputs and the intensity of said beam being different for said first and'second portions; means for deflecting said beam to impinge said beam successively upon said first and second portions of said beam interceptive structure; a source of an image signal comprising components Within a predetermined frequency range; means responsive to said image signal to modulate the intensity of said beam to control the light emission from said iiuorescent screen structure, said modulation also producing variations in the outputs of said portions comprising frequency components within said range; a source of carrier signal of a frequency external to said range; means for modulating the intensity of said beam in accordance with said carrier signal, said last-named modulation and the successive impingements of said beam upon said rst and second portions cooperating to produce variations in said outputs comprising frequency components external to said range; and means for deriving from said outputs a signal representative solely of variations in said outputs comprising frequency components external to saidI range.

7. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptive structure including a fluorescent screen structure and also having first and second portions, said portions being responsive to beam impingement to produce outputs which vary in proportion to the variations in beam intensity, the factors of proportionality between the output and the intensity of said beam being different for said first and second portions; means for delecting said beam to impinge said beam successively upon said first and second portions of said beam interceptive structure; a source of an image signal comprisingV components Within a predetermined frequency range; means responsive to said image signalto modulate the intensity of said beam to control the light emission from said fluorescent screen structure, said modulation also producing variations in the outputs of said portions comprising frequency components Within said range; means for modulating the intensity of said beam at a frequency external to said range, said last-named modulation and the successive impingement of said beam upon said first and second portions cooperating 22 to produce variations in said outputs comprising frequency components external to 'said range; and means for deriving from said outputs a signal representative solely of variations in said outputs comprising frequency` components external to said range.

8. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptive structure including a fluorescent screen structure and also having first and second portions, said portions being responsive to beam Vimpingement to produce outputs which vary in response to variations in beam intensity, the relationship between said outputs and the intensity of said beam being different for said first and second portions; means for deflecting said beam to impinge said beam successively upon said first and second portions of said beam interceptive structure; a source of an image signal comprising components within a predetermined frequency range and having recurring time spaced portions representative of intelligence, said source of image signal being controllable to vary the rate of recurrence of said portions; means responsive to said image signal to modulate the intensity of said beam to control the light emission from said iiuorescent screen structure, said modulation also producing variations in the output of said portions comprising frequency components Within said range; means for modulating the intensity of said beam at a frequency external to saidy range; said last-named modulation and the successive impingement of said beam upon said first and second portions cooperating to produce variations in said outputs comprising frequency components external to said range; and means for deriving from said outputs a signal representative solely of variations in said outputs comprising frequency components external to said range.

9. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptive structure including a fluorescent screen structure and also having first and second portions, said portions being responsive to beam impingement to produce outputs which vary in response to variations in beam intensity, the relationship between said outputs and the intensity of said beam being diiferent for said first and second portions; means for deflecting said beam to impinge said beam successively upon said first and second portions of said beam interceptive structure; a source of an image signal comprising components within a predetermined frequency range; means responsive to said image signal to modulate the intensity of said beam to control the light emission from said fluorescent screen structure, said modulation also producing variations in the outputs of said portions comprising frequency components Within said range; means for modulating the intensity of said beam at a frequency external to said range, said last-named modulation and the successive impingements of said beam upon said first and second portions cooperating to produce variations in said outputs comprising frequency components external to said range, said variations comprising a carrier component of frequency determined by said last-named modulation and modulation components of frequency determined by the rate of traversal of said rst and second portions by said beam; and means for deriving from said outputs a signal representative solely of said modulation components.

10. In a cathode ray tube system: a cathode ray tube comprising a sourc'e of an electron bea and; `a,;;beam,; interceptive structure `including- ,a iuorescent screen;structure` and also havingrst and secondi-portions ofiV ,different predetermined secondary; electron emissivity; means for-danesi;- ingfsaidbeam to impinge said Ybeam successively upon said iirst and second portions of-.said-beam inlcrceptivestructure; ai sourceo'fvan image sig- Ila .icoinprisingdcomponents Within a'predeterminedffrequency `range; .rn eans responsive to said image signal to modulatethe intensityfof said beanry to controlQthe-light emission from said fluorescent Y screen V- structure;y f saidv`r modulation alsoproducing-variations infthe secondary Aelectronemission ofvrsaid portions comprising Vfrequencytcomponentsfwithinsaid range; means for modulating the intensityof` said beamat a frequency externaltosaidrange, said last-named modulation and -theysuccessive impingementof saidbeam u-pon 'saidf-first -and second-portions cooperating toproduce variations in-said. second.- aryelectron emissioncomprisingfrequency components external to.saidrange; and means/for deriving from said; secondary electronY emission a signalrepresentative solely of variations 4in said secondary electronemission comprising frequency components-external? tosaid-range. Y f idljaAfcathoderay tubesysteml comprising: a cathode may tube,includingja= source.. of 4an electronbeam, afbeamfinterceptive structure having first and-secondportions rif-different predeterminedisecondary electron emissivity,A and an velectrode -arigangedfvtofintercept the secondary electrons ernitted'bysaid structure means for periodicallyrdeflecting said beam across-saidstructure ,s o; ,y as tqgfimpinge said beam-f successively upon said -rst and" second i portions; a rsource ofan imagesignal-v comprisingacomponents- PWithint a predetermined.- .frequency; means -responsive to said maga signal-fisofmodulate gthe- `intensity of said beam; means for modulating-.the.intensity of; saidbeamwvith a-carrie1=signa1 having, -a 'frequency external to said range, said last-named modulationf and the successive impingements of said beam upon 4said-.iirst andsecondaportions cooperating t to, :produce variations in .t secondary electron `emission comprising' frequency componentseXternal-to said range; and means for deriving from-said'variations/:a voltage which -var-ies solely -in proportion` 'to s lvariationsffinfsecondary electron emissionrcomprising frequency lcomponents external-.to saidrange.Y ,f 1,; l.l.2. Avsystem according-.to claim 11 and comprisingV additionalmeans/supplied with saidlastnamed voltage andyvith said carrierA signaland operative. to, producea heterodyne component thereof which.- is representative "solely `ofY L Var-iationsin secondary. electron emission from said screen structure-,as saidbeam traverses said first andsecond portions. f l3.v.A.catliode. ray tube system comprising: a cathoderay tube including asource o f. an elec tron beam,Y a beam interceptive .structure .having Iirst ,and .secondi portionsfzof diierent.` :predetermined. secondary electron emissivity, Aand an elec trode, arranged to .intercept secondary. electrons ,emitted by said structure means: forfperiodically deflecting saidbeam'across said structuresoasto impinge said beam successivelyfupon.said-fiirst and :second portions; a source of an image-signal comprising componentswithina predetermined vfrequency range; means responsive to said image signalto modulate -the intensityof said beam.; means for. modulating the intensityof said beam With a carrier signal having a frequencyexternal to said range, said last-,named modulation and tnefsuccessive impingements of said beannupcn saidrstandsecondportions cooperating to produce variations; inthe[secondaryV electron emission comprising frequency .components yexternal to said rangevsaidyariationsv:comprising a ca rri er-I IVcomponent ,of frequency Adetermined. by said last-named modulation and. modulation compo; nents ot trequency determinedby lthe rate of trav.`` ersal oufqsaid iirstandsecond portions by said beam; and means for .deriving from said second.:

ary. electronemission4 la signal representative solely ofsaid modulation components. 'y 1 t 14, Arcathode raytube system comprising: a cathode vraytuloeincludinga-scurce of an` elecf tronbeam, t afbeaminterceptive structure having rst and second-.portions Lof different predeterf mined-secondary electron emissivity, and anY electrode arranged to intercept secondaryelectrons emittedby said structure; means-.for .periodicallydeecting said beam across said structure-so as tofimpinge said Hbeam successively upon said first andsecond portions;A asource offanimage signalcomprising components within a predetermined frequencyrange; means responsive to said image signalY toY modulatethe lintensity, of said beam; means for modulating the intensity of said beam with la carrier ,signal having a .frequency external Ito said :rangeqsaid last-named modular tion and .the successive. i--mpingementsV of Asaid beam. upon saidfirst and secondportions cooperating to .produce rvariations in thesecondary electron .emission vcomprising .freduency compo? nents externaltosaid` range, said variations.com prising av carrier component vof frequency determined by said last-named-modulation. and aplurality of modulation sideband components of frequencies determinedlbyv the, rate. ofntrafversallof said nrst and second portionsby. said beam.;T and means for` deriving f rom,.said.outputs a vsignal representative .solelyr ottone'A of said modulation components. ...3.

15..Inacathode' ray tube system: a cathode raytube comprising v as source ofonelec-tron beam and :a-fbeam interceptive structureY including .a plurality..of A parallelly disposedT ,strips` ofluorescent material vresponsive toielectron beam impingement -to produce :diiierent visible indications 1,;hereof and .alsdhaving first and-second portions arrangedv in predetermined geometrical relationship With respect to said fluorescentstrips, said portions having ldiiverentV secondary i electron emissivitiesgmeans for deflecting said beam -to impinge' said -4 beam successively. upon diierent ones ofsaid iluorescent strips and also to impinge said beam successively/'upon said first and second portions; a` sourcefof an imagesignal comprising components within apredetermined .frequency rangeandvbeing representative of diierent in telligence at ltime-spacedy intervals recurring at' a predetermined rate, said: source vbeing-controllable ,tovary'saidrate of recurrence; a source of -a carf rier. signalofI frequencyexternal to said range; means responsiveto--both said imagev signal and said -carrier signal to Jmodulate the intensity of said .b eam, the `modulation vof said lbeam and the successive fimpingement of said beam upon said` rst-and second .portionsl ofsaid screen structure producinggvariations in `the secondary 4electnm emission from. saidscreen structure comprising frequency confiponentsexternal to said range;` meansfor deriving from said secondary electron emission a signal representative solely of variations saidemissioncomprising lfrequency componentsV external-to saidr range; andfmeans 25 for utilizing said derived signal to control said source of image signal to vary the said rate of recurrence of intelligence representative interva s.

16. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptive structure including a plurality of parallelly disposed strips of fluorescent material responsive to electron beam impingement to produce light of different colors and also having first and second portions arranged in predetermined geometrical relationship with respect to said fluorescent strips, said portions having different secondary electron emissivities; means for deflecting said beam transversely of said strips so as to impinge said beam successively upon diierent ones of said strips in predetermined order and also to impinge said beam successively upon said rst and second portions; a source of an image signal comprising components within a predetermined frequency range, said image signal being representative of intelligence respecting said different colors at time spaced intervals recurring at a predetermined rate and occurring in said predetermined order, said source being controllable to vary said rate of recurrence; means responsive to said image signal to modulate the intensity of said beam said modulation and successive impingement of said beam upon said rst and second portions cooperatively producing variations in secondary electron emission from said screen structure having frequency components Within said range; a source of a carrier signal of frequency external to said range; means responsive to said carrier operatively producing variations in the second- L ary electron emission from said screen structure having frequency components external to said range; means for deriving from said secondary emission a signal representative solely of variations in said emission comprising frequency components external to said range; and means for utilizing said last-named signal to control said source of image signal to vary the said rate of recurrence of color representative image signal intervals.

17. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptive structure including a plurality of parallelly disposed strips of fluorescent material responsive to electron beam impingement to produce different visible indications thereof and also having first and second portions arranged in predetermined geometrical relationship with respect to said fluorescent strips, said portions having different secondary electron emissivitles; means for deflecting said beam to impinge said beam successively upon different ones of said uorescent strips and also to impinge said beam successively upon said first and second portions; means for producing an image signal having frequency components within a predetermined frequency range and being representative of di'erent intelligence at time-spaced intervals recurring at a predetermined rate, said last-named means comprising a source of carrier signal of frequency external to said range, means cooperating with said source to produce a signal of carrier signal frequency and representative of said di'erent intelligence at time-spaced intervals, means responsive to said carrier signal to modulate the intensity of said electron beam, said modulation and successive impingements of said beam upon said rst and second portions of said beam interceptive structure producing variations in secondary electron emission from said structure having frequency components external to said range, means for deriving from said variations a signal representative solely of variations having frequency oomponents external to said range, a mixer supplied with said derived signal and with said intelligence representative signal of carrier frequency, said mixer being operative to produce heterodyne components of said supplied signals, and means for deriving from said mixer heterodyne frequency components within said predetermined range; and means responsive to said mixer derived components to modulate the intensity of said beam.

18. In a cathode ray tube system: a cathode ray tube comprising a source of an electron beam and a beam interceptive structure including a plurality of parallelly disposed strips of fluorescent material responsive to electron beam impingement to produce different visible indications thereof and also having rst and second portions arranged in predetermined geometrical relationship with respect to said fluorescent strips, said portions having different secondary electron emissivities; means for dellecting said beam to impinge said beam successively upon different ones of said fluorescent strips and also to irnpinge said beam successively upon said rst and second portions; a source of an image signal comprising components within a predetermined frequency range and being representative of different intelligence at time spaced intervals recurring at a predetermined rate; a source of a reference signal Whose frequency is indicative of the rate of recurrence of said intervals of said image signal; a source of a carrier signal of frequency external to said range; means responsive to said carrier signal to modulate the intensity of said beam, the modulation of said beam and the successive impingements of said beam upon said rst and second portions of said screen structure producing variations in secondary electron emission from said screen structure comprising frequency components external to said range; means for deriving from said secondary emission a signal representative solely of variations in said secondary emission comprising frequency components external to said range; a rst mixer supplied with said derived signal and with said reference signal; means for deriving from said first mixer a heterodyne component produced by mixing of said derived component and said reference signal; a second mixer supplied with the said heterodyne component derived from said first mixer and with said image signal; means for deriving from said second mixer a heterodyne component produced by mixing of the said supplied heterodyne component and image signal; and means responsive to said last-named heterodyne component to modulate the intensity of said beam with a signal proportional to said lastnarned heterodyne component.

EDGAR M. CREAMER, JR. MELVIN E. PARTIN.

References Cited in the file of this patent UNITED STATES PATENTS Weimer Mai. 13, 1951

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